Frequently in the life of a well there comes a need to create additional lateral from a main bore or other branch bores to increase production from a producing zone or to exploit new zones or for various other purposes such as fluid injection to stimulate production from other wells. When this need arises a procedure is undertaken that involves setting and anchor that can receive a whipstock and using MWD equipment as an aid to obtain proper orientation of the whipstock. The whipstock is initially connected to a series of mills that are rotated to break loose from the now anchored and oriented whipstock. The whipstock diverts the mills into the casing wall to start a window or opening in the casing for a lateral exit. Equipment has been developed to produce the window in a single trip.
Frequently, the whipstock is left in the well after the window is produced. This creates an expense for the operator as the operator must buy all service equipment left in the well. Another issue in traditional window milling operations is the cost of the service. The milling through the casing wall creates cuttings that need to be circulated out of the well. Problems with cuttings or with milling are also possible and sometimes the window is not properly formed or the lateral exit angle doesn't turn out as planned.
While eliminating all potential problems in window milling is an ideal, the present invention addresses a part of this process and seeks to find a reliable and low cost way to be able to have a suitable diverter downhole for the mills and avoid having to manufacture and run a whipstock into position. In essence, the invention addresses ways to actually use the casing itself as a diverter and position a portion thereof as such where the drilling of the lateral will not even require milling up a long window in the casing and the attendant issues of dealing with cuttings that such milling raises. As such the concept represents a dramatic departure from prior techniques of window milling and production of laterals through them.
As an example, explosives have been used to blow out a part of the casing with shaped charges such as shown in U.S. Pat. No. 5,636,692. In this case, the mill supported explosives right above a whipstock. One issue with trying to make a complete or nearly complete window with explosives has been the debris generated from the process and how to effectively remove it from the wellbore. Other attempts have simply blown through casing to create an opening in it but in so doing created a fair amount of debris that potentially undermined subsequent operations.
The present invention while using explosives reduces or eliminates such issues and finds a way to use the casing itself as a diverter while allowing the lateral to begin without having to mill up a window in the casing. The present invention also affords a way to produce a window through which a lateral can be drilled by a technique that allows a portion of the tubular to be cut and bent back on itself to from a window without the debris that characterized prior attempts to make windows with explosives, chemicals, abrasive jets or other cutting or milling tools. These and other advantages of the present invention will be more readily apparent to those skilled in the art from the description of the preferred embodiment, the drawings and claims that appear below.